Image guided medical and surgical procedures utilize patient images obtained prior to or during a medical procedure to guide a physician performing the procedure. Recent advances in imaging technology, especially in imaging technologies that produce highly-detailed, two, three, and four dimensional images, such as computed tomography (CT), magnetic resonance imaging (MRI), fluoroscopic imaging (such as with a C-arm device), positron emission tomography (PET), and ultrasound imaging (US) has increased the interest in image guided medical procedures.
Typical image guided navigation systems generally require dynamic reference frames to track the position of the patient should patient movement occur during the assisted procedure. The dynamic reference frame is generally affixed to the patient in a generally permanent or immovable fashion. The dynamic reference frame may also be used as a fiducial marker and may, therefore, be attached to the patient during the acquisition of pre-operative images. This enables the image space to be aligned with patient space during the navigated procedure. For example, with relation to a cranial procedure, the dynamic reference frame can be attached to the skull by a bone screw. For other procedures the dynamic reference frame may be fixed to other boney portions also with bone screws. Regardless, the dynamic reference frame may include a portion that is fixed to the patient during the acquisition of the pre-operative images and remains attached until the procedure is complete to insure proper and accurate correlation between image space and patient space. Requiring that the dynamic reference frame be attached to the patient during the time that the pre-acquired images are acquired until the procedure actually takes place may be uncomfortable.
The dynamic reference frame may, then be used to assure that images of a patient, such as pre-acquired or atlas images, may be registered to the patient space. Generally this registration also allows for tracking of various instruments during a procedure. The tracked instruments will generally include portions that may be tracked and super-imposed over acquired or modeled images of the patient.
Various instruments may be used during an operative procedure that are desired to be tracked. Even if images are acquired, either intra-operatively or pre-operatively, the instrument is generally illustrated, and superimposed on the captured image data to identify the position of the instrument relative to the patient space. Therefore, the instrument may include detectable portions, such as electromagnetic coils or optical detection points, such as LEDs or reflectors, that may be detected by a suitable navigation system.
Size considerations generally make it difficult to position the tracking sensors near a portion of the instrument to be positioned within the patient, such as the distal tip. Because of this, the tracking sensors are generally positioned within the handle of the instrument. Therefore, complex calculations and a degree of error may exist to determine the exact position of a distal end of the instrument relative to the position of the detectable sensors. Also the instruments may flex unexpectedly so that the known dimensions are no longer true dimensions of the instrument. Therefore, it may be desirable to provide sensors substantially near the distal tip or end of an instrument positioned within a patient.
The tracking of various sensor portions, such as electromagnetic coils, may require the transmission of a current or a voltage to or from the sensors. Therefore, an electrical potential is provided to an instrument that is often positioned within a portion of the patient's anatomy, which may include various portions such as the cardiac area, neurological area, and other areas of the patient. In order to provide separation of these potentials from the patient, it may also be desirable to isolate the potentials from the patient.